In the agricultural areas, particularly with orchids, frost damage can occur to vast areas with consequential dire results to the orchardist. As is well known this occurs due to the freezing of the moisture in the plant leaves which causes rupture and destruction of the cells of the leaf. This can occur on various plants and trees, not only particularly frost sensitive plants, etc. as tomatoes, but also in other orchid plants such as citrus trees, avocados, grape vines and the like. With grape vines, damage can occur with late frosts affecting the buds, for even with grape vines the bunch is in effect formed in the bud, and frost can affect the fruiting buds and thus the crop can be severely damaged at this early stage of the bud development. Also damage can occur to the leafing buds so that the desired laterals are not formed thus affecting the vine growth for a number of years.
Attempts to alleviate the frost damage have been made by the provision of large fans blowing air horizontally over the area to be protected, these fans being axial flow fans with their axes generally horizontal to the ground.
While these are satisfactory to some extent, they are limited in their application in that the area protected is only that directly in front of the large fan or propeller type unit.
It is well known that in frost conditions a temperature inversion layer occurs, with the cold air being situated close to the ground while at a higher elevation there is a layer of warmer air. This inversion layer can occur from a few centimeters or a meter above the ground or to a higher level such as ten or twenty meters.
It is an object of the invention to provide a means whereby the warmer air above the inversion layer is drawn downwardly and then dispersed to achieve a frost nullifying effect, not only by the provision of the warmer air, but by providing air movement, however small, over the areas to be protected.